This invention relates generally to the field of superconducting ceramics and particularly to manufacturing methods for making superconducting ceramics.
It has long been known that metals such as mercury and lead, intermetallics such as NbNd, Nb.sub.3 Ge and Nb.sub.3 Ga and ternary materials such as Nb.sub.3 (Al.sub.0.8 Ge.sub.0.2) demonstrate superconductivity. However, the transition temperature of such long known superconducting materials cannot exceed 25.degree. K.
In more recent years, superconducting ceramics have attracted widespread interest. A new material was first reported by researchers at the Zurich laboratory of IBM Corp. as Ba-La-Cu-O-type high temperature superconducting oxides. Subsequently, La-Sr-Cu(II)-O-type superconducting oxides were also proposed. Another type of superconducting material that has been found is (YBa.sub.2)Cu.sub.3 O.sub.6-8. By virtue of the fact that these superconducting ceramics form a quasi-molecular atomic unit in a crystalline structure whose unit cell is constructed with one layer in which electrons have essentially one-dimensional motion, whereas only three-dimensional electron conduction occurs in the long known materials mentioned above, higher transition temperatures are achieved.
Much work has been undertaken by researches in this field who have endeavoured to elevate Tco, the temperature at which resistance vanishes, above the levels previously obtained and preferably above the boiling point of nitrogen (77.degree. K.) or even higher. As described in our European Patent Application No. 87309081.5 we have investigated superconducting ceramics materials having the stoichiometric formulae (A.sub.1-x B.sub.x).sub.y Cu.sub.z O.sub.w, where A represents one or more elements of Group IIIb of the Periodic Table, e.g. the rare earth elements, and B represents one or more elements of Group IIa of the Periodic Table, e.g. the alkaline earth elements including beryllium and magnesium, and in the continuation of these investigations we have discovered that the existence of voids and grain boundaries in superconducting ceramic materials makes it difficult to obtain an elevated Tco.